The invention disclosed herein relates generally to decoupling capacitors for use with integrated circuits.
In the past decoupling capacitors for integrated circuits have sometimes been separate devices mounted on a printed wiring board and wired across the power supply and return connection to the dual in-line or other type integrated circuit package.
Inductance is dependent on the loop area through which current flows and the magnetic flux through the loop. Voltage drop due to inductance is equal to ##EQU1##
In the past approach of a separate capacitor on the circuit board the length of the path that the current must flow through from the capacitor to reach the chip contributes to the voltage drop due to ##EQU2##
Another past approach has been to mount a decoupling capacitor on the chip package to reduce the lead length between the capacitor and the chip. While past methods provide adequate decoupling for many applications, there are other applications that require improved decoupling.
An example of such an application is the need for certain integrated circuit devices to be insensitive to being bombarded by ionizing radiation. A basic effect of the ionizing radiation is to generate electron-hole pairs in the semiconductor material. In an integrated circuit having a power supply voltage reference and a ground reference, the effect of being irradiated is to create a high current flow in the chip between the voltage reference and the ground reference. The further effect is for current flowing from the power supply to encounter inductance in the connecting leads from the power supply. The result is that the on-chip voltage essentially collapses.
A solution is to place a capacitor across the integrated circuit as close as possible to the integrated circuit so that the capacitor is charged to the chip power supply voltage. Then when a transient due to radiation or any cause occurs, the board capacitor is available to supply current instantaneously to the integrated circuit. Thus a need exists for a decoupling device that can be placed as close as possible to the integrated circuit.